In recent years, owing to widespread use of portable personal computers and portable phones, it has been highly demanded to develop a lithium ion secondary battery having a higher capacity and a reduced size. If a lithium ion secondary battery has a higher capacity, reduction in size of a battery material can be facilitated, and hence the development of an electrode material for a lithium ion secondary battery is urgently needed in order to accomplish the higher capacity.
High potential type materials such as LiCoO2, LiCo1-xNixO2, LiNiO2, and LiMn2O4 are each widely used for a positive electrode material for a lithium ion secondary battery, and on the other hand, a carbonaceous material is generally used for a negative electrode material. These materials function as electrode active materials that reversibly store and release lithium ions through charge and discharge, and construct a so-called rocking chair type secondary battery in which both electrodes are electrochemically connected through a non-aqueous electrolytic solution or a solid electrolyte.
Examples of the carbonaceous material used as a negative electrode material include a graphite carbon material, pitch coke, fibrous carbon, and high-capacity type soft carbon prepared by low-temperature firing. However, the carbonaceous material has a relatively small lithium insertion capacity, and hence involves a problem in that a battery using the carbonaceous material has a low capacity. Specifically, even if a lithium insertion capacity in a stoichiometric amount is attained, the upper limit of the capacity of the battery using the carbon material is about 372 mAh/g.
In view of the foregoing, there is proposed a negative electrode material containing SnO as a negative electrode material that is capable of storing and releasing lithium ions and has a higher capacity density than the carbon-based material (see, for example, Patent Literature 1). However, the negative electrode material described in Patent Literature 1 involves a problem in that the material is not capable of sufficiently abating the volume change thereof attributed to the storage and release reactions of lithium ions, and thus is extremely poor in charge-discharge cycle performance.
In view of the foregoing, there are proposed a negative electrode material formed of a complex oxide mainly containing tin oxide and a method of producing the negative electrode material by a melting method (see, for example, Patent Literature 2). In addition, as a method of producing a negative electrode material which is formed of a complex oxide containing tin oxide and silicon oxide, is homogeneous, and has a large specific surface area, there is proposed a production method using a sol-gel method (see, for example, Patent Literature 3).